The use of mustard agent would mark an upgrade in Islamic State’s battlefield capabilities, and a worrisome one given U.S. intelligence fears about hidden caches of chemical weapons in Syria, where Islamic State controls wide swaths of territory.

It raises new questions about the evolving threat posed by Islamic State and the ability of U.S. allies on the ground to combat it. Frontline Kurdish, Iraqi and moderate Syrian forces say they aren’t getting enough U.S. support now to counter Islamic State’s conventional capabilities.

Officials say these forces may need specialized equipment and training to help protect them against unconventional weapons if they become a fixture on the battlefield.

Retired Lt. Col Bill Cowan said on “Happening Now” that it’s possible that ISIS has much more dangerous chemical weapons than mustard gas.

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